"I told him point blank: there is nothing I can tell you to make you happy. I have to be very careful what information I volunteer, because if I talk too much, you get angry. And now if I don’t talk enough, you get angry."
It was over for her right here.
She came across as nervous, evasive, defensive and then antagonist. She is leaking privilege all over this post.
And she really was treated just like everyone else in detention. Of course she wasn't a terrorist, but she was being detained and that never feels good, nor is a hotel. That's reality.
Border agents have enormous latitude. Your attitude matters when dealing with any authority. Maybe it shouldn't, but there are roles here and when you step out of the expected role you start triggering something. How would she have spoken to a judge in a court of law?
Sure, she didn't deserve this, but she didn't do anything to improve her situation, either. It doesn't matter how little sleep she had, or how virtuous her cause, or whether she is a big deal in her industry. It's naive to think that any of this is relevant, frankly.
No border guard cares about your self-perception of virtue. They are about tax avoidance and illegal immigration. And just like a pediatrician develops the ability to instantly detect a "funny looking kid," a border guard who sees thousands and thousands of people has similar behavioral flags.
"I'm here for a conference."
"What topic?"
"Web development."
"How long are you staying?"
"One week."
"What else will you be doing?"
"I will do a little sightseeing while I'm here."
"Have a good stay."
CLUNK
No lies, nothing cagey in this. There are bins and categories; don't do anything that puts you into a special bin. It's not that hard. Be like the other thousand people they saw this week who are attending a conference.
I travel all over the world to speak at conferences. Apart from China and Russia, I never mess around with invitation letters or special papers. I am calm and matter of fact, and so is the border agent. Each of us plays our role and then we move along.
"I'm here for a conference." Which is true.
FFS, I live in the US and my wife (a Finn) has a UK permanent residency and works in London. I go back and forth about six times a year, I stay for weeks. When they ask the purpose of my visit I simply say, "I'm visiting my wife." I'm friendly and calm.
"Are you planning to immigrate?"
"Maybe some day."
I thought being married to a UK resident would be a flag, but it actually isn't. They care about illegal immigration and tax avoidance because that is their job. I am calm, even friendly, and I don't trigger any suspicion. I finally applied for Frequent Traveler status and now just use the UK /EU electronic gates. That wasn't hard, either. Didn't even need to give a reason for that!
Don't be defensive, don't provoke suspicion, don't volunteer unnecessary details. Don't lie, but be shrewd about this situation. Don't trigger special handling.
OP does seem to express a bit of a special snowflake tone in her piece. Privilege. Not a good vibe once they are triggered. Earnest humility is the tone you want to adopt. That is proper etiquette given the real power differential. This isn't being subordinate, it's just like being in court. Respect the judge. This border agent is actually judging you--that's their job.
None of what happened to her was personal and no one here was ever going to say, "well, you seem like a decent person doing good work; I guess we can just fudge this a teeny bit." They can't and won't do that, and frankly, her attitude probably evoked a little contempt, thus reducing her chances for even what teeny latitude she might have had.
Her experience was exactly what people who expect to get a little special handling have when they encounter faceless rule-driven systems. "But this is ME! Why are you doing this to ME?"
People without privilege have no such illusions and understand these situations.